Various pneumatic means have already been proposed to loosen and unravel textile yarns. For instance, devices are known which comprise a channel in which the yarn to be untwisted is placed and in which one or two tangential jets are blown and generate a swirl for untwisting a yarn as disclosed in U.S. Pat. No. 4,408,442. A device is known, as disclosed in U.S. Pat. No. 4,549,392, to loosen textile yarns which comprises a cylindrical channel for receiving the thread and in which an air jet is injected and directed against a baffle plate located in the channel and capable of forming two symmetrically oriented but counter-rotating whirls. Depending on its twist configuration the yarn is subjected to one or the other of the whirls in order to be untwisted.
It is known that with many kinds of yarn, namely open end or ply yarn, untwisting is not sufficient to achieve unravelling because the fibers are not all uniformly twisted and, in some cases e.g. with ply yarns, they are twisted in opposite directions. In this case, it is not readily possible to loosen, unravel and open up the yarn end by a pneumatic untwisting operation. It is known now that unravelling and opening up the ends of yarns to be spliced together is essential for obtaining appropriate strength and good visual aspect of the spliced yarn. It has been noted in this connection that if the ends of hard-to-untwist yarns are subjected to a pneumatic action limited to an untwisting and pulling effect, the desired result is not attained. Indeed, if a blocking effect occurs, because for instance the fibers are not parallel like in an open-end yarn, the uni-directional untwisting action is not effective to loosen the blocked fiber portion and the pull constantly applied to the end tends to further tighten the fibers in the blocked portion.
Consequently, the various proposed solutions are inadequate to properly settle this problem.
Another solution still exists, from EP-A-0.053.093, in which it is proposed to subject the thread to vibrations for reducing the friction between the fibers and for decreasing the risks of blockage. For this, one vibrates a flexible element in an air stream. This route gives results but still has limits. Furthermore, the vibrating element may wear out with time and should be periodically replaced.